With broadcast antennas, such as circularly polarized wave antennas, it is always desirable to broadcast over a wide frequency band at a high radiator power level. Also, in some environments, icing of the antennas is inevitable and this icing affects the transmission (tuning) characteristics of the antennas.
It is the object of the invention to broadcast circularly polarized waves over a frequency band wider than typical broadcast antennas, at a per radiator power level higher than typical broadcast antennas, with ice susceptibility in an unprotected bay lower than typical broadcast antennas.
The above and other objects of the invention are attained by an antenna construction including as the basic radiating elements a pair of conducting arms having portions forming a normal mode helix with one arm interrupted by an insulator to permit the connection of an internal feedline. The normal mode helix is a broadband radiator. The bandwidth in this case is enhanced by the large size (.lambda./39 diameter) of the conducting arms. This large arm size also allows a larger feedline to fit inside the individual radiator, thereby increasing the power input rating. In a preferred embodiment, in this case at 100 MHz, 40 kW CW would be the input power rating.
Ice susceptibility is reduced by covering the sensitive feed point with an insulator and by spreading out the effect of ice with large diameter conducting arms.
Broadly, my invention, in a preferred embodiment, provides a frequency band of about 3 MHz wide compared to a prior art antenna of 0.5 to 1.0 MHz. Also, the antenna of the invention is 40 kilowatts input power versus 30 kilowatts of the prior art. Further, the feed structure of the antenna is isolated from icing.